Two-thirds of equine veterinarians fear that frequent injections could damage the joint
Joint inflammation and osteoarthritis (OA) are common in sporting horses, often leading to lameness, poor performance, and economic loss. Veterinarians can provide symptomatic relief of joint discomfort caused by OA through intra-articular injections with a variety of drugs. Examples include corticosteroids (eg, triamcinolone acetate, methylprednisolone acetate), hyaluronic acid, polysulfated glycosaminoglycans, and various biological therapies, such as stem cells, platelet-rich plasma (PRP), autologous conditioned serum (ACS, protein interleukin-1 receptor antagonist, IRAP), and autologous protein solution.
Which drugs veterinarians inject, into which joint, and how often it can be administered into that joint are factors ultimately determined by the veterinarian using their own clinical experience. Therefore, these options are largely based on anecdotal evidence rather than scientific guidelines. In other words, there are no hard and fast rules regarding joint injections due to the lack of direct comparisons of the various treatment options.
To gain a deeper understanding of how veterinarians administer drugs to the joints, an American Association of Equine Veterinarians (AAEP)-approved survey was conducted in 2019. That data was subsequently analyzed by Dr. Gustavo Zanotto of the Department of Large Animal Clinical Sciences at Texas A&M University College of Veterinary Medicine and Biomedical Sciences. Dr. David Frisbie, from the Department of Clinical Sciences at the Colorado State University College of Veterinary Medicine and Biomedical Sciences, co-authored the study.
Zanotto recently presented the results at the 2021 AAEP Annual Convention held in Nashville, Tennessee. In total, 407 equine veterinarians participated in the survey, most of whom worked with racehorses (Thoroughbreds, Quarter Horses) and Warmbloods. The veterinarians had extensive clinical experience (>20 years). Here are some of the most important points gleaned from the survey applicable to Thoroughbred racehorses:
Injection frequency
About two-thirds of veterinarians were concerned about treating joints too frequently with corticosteroids for fear of causing damage, presumably to articular cartilage. "About 75% of responding veterinarians said they believe joints can be damaged if treated too often. The majority believe that it can be injected only once every six months, while 30% indicate that it can be done every three months," Zanotto said.
Despite these beliefs/recommendations suggested by survey practitioners, Zanotto explains: "There is no strong scientific evidence regarding the minimum frequency of joint injections."
Selection of corticosteroids
Triamcinolone and methylprednisolone are the drugs most frequently used by equine veterinarians in high- and low-motion joints, respectively. However, almost three-quarters of veterinarians still believe that triamcinolone is likely or very likely to contribute to laminitis. As a result, respondents reported using limited amounts of triamcinolone, both in a single joint and as a total dose per horse. According to the survey, most veterinarians reported using 5 to 10 mg of triamcinolone in a single joint and 20 to 40 mg of methylprednisolone. Most practitioners use less than 40 mg of triamcinolone per horse, with about 50% using no more than 18 mg of triamcinolone per horse.
However, based on scientific evidence, Zanotto said that "triamcinolone does not appear to increase the risk of laminitis in healthy horses, and a safe total body dose has not yet been established."
Antibiotic use
In this survey, 55.6% of veterinarians admitted to always using an antibiotic such as amikacin when injecting medication into a joint. Perhaps the most disturbing fact was that the number of veterinarians using an antibiotic when treating a joint increased compared to a similar survey conducted in 2009. "This increased use of antibiotics is an alarming finding because there is evidence that amikacin is toxic to cartilage cells, as well as the greater concern of the development of resistance to antibiotics", explained Zanotto.
The reasons veterinarians cited for using intra-articular antibiotics were poor environmental conditions and "coincidental corticosteroid injections." Such statements should give us pause for two main reasons. First, Zanotto pointed out that there really isn't any evidence to support the notion that corticosteroid-treated joints have an increased risk of infection. Second, there is no evidence that the environmental conditions in which joints are treated contribute to joint infections. In fact, according to Dr. Lynn Pezzanite of Colorado State University, joint infections are extremely rare.
During her presentation at the 2021 AAEP Annual Convention, Pezzanite explained data she retrospectively collected from joint injections performed between 2014 and 2018. In total, 3,866 synovial injections were performed on 1,112 horses during 1,623 sessions. Of these, 643 sessions were held in the field. The Pezzanite data revealed that the risk of sepsis (infection) was similar between joints injected in the field and in the hospital and between joints that had or had not been treated with an antibiotic. Overall, the frequency of sepsis was 1 in 967 injections or about 0.1%.
Biological therapies gain ground
Perhaps due to equine veterinarians' increasing familiarity with the various biological therapies available on the market, as well as the perceived benefits of such therapies, their use is increasing. According to the survey, IRAP is the most popular biologic therapy, followed by PRP, autologous protein solution, stem cells, and bone marrow aspirate/concentrate. Cost is an important determining factor in which biological product is ultimately used.
In summary, despite the frequency with which joint injections are performed, there is still a profound lack of evidence-based guidance regarding injection frequency and recommended doses, particularly for corticosteroids. However, one of the most alarming findings is the excessive and unnecessary use of antibiotics in routine joint injections for prophylactic purposes.
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